Method For Manufacturing Metal Composite Sintered Body

ABSTRACT

A method for manufacturing a metal composite sintered body includes: a molding step of injection-molding a first molded product and a second molded product from a kneaded product of a metal powder and a binder; an assembling step of fitting the first molded product to the second molded product without performing a solvent degreasing treatment to form a composite; and a heating step of subjecting the composite to a thermal degreasing treatment and a sintering treatment, in which the first molded product and the second molded product have fitting portions that fit to each other, at least one of the fitting portion of the first molded product and the fitting portion of the second molded product has a tapered shape, in the assembling step, a maximum meshing when the fitting portions are fitted to each other is 0.002 mm or more and 0.010 mm or less, and a content of the binder in the kneaded product is 2 mass % or more and 20 mass % or less with respect to a total amount of the kneaded product.

The present application is based on, and claims priority from JP Application Serial Number 2020-059819, filed Mar. 30, 2020, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a method for manufacturing a metal composite sintered body.

2. Related Art

In the related art, a composite sintered body obtained by assembling a plurality of metal injection molded products is known. For example, JP-A-2010-236042 discloses a method for manufacturing a metal composite sintered body in which a plurality of metal injection molded products subjected to a degreasing treatment with a solvent are adhered and then subjected to a sintering treatment for bonding.

However, the method for manufacturing a metal composite sintered body described in JP-A-2010-236042 has a problem that workability is likely to be lowered and it is difficult to improve quality of the metal composite sintered body. Specifically, the metal injection molded products are subjected to the degreasing treatment with the solvent before assembling a composite molded product. Since a binder is removed or reduced by the degreasing treatment, the metal injection molded products are likely to be brittle, which may make it difficult to handle and reduce the workability. Further, when the metal injection molded products become brittle, damage is likely to occur and the quality may be reduced. That is, there is a demand for a method for manufacturing a metal composite sintered body having excellent workability and stable quality.

SUMMARY

A method for manufacturing a metal composite sintered body includes: a molding step of injection-molding a first molded product and a second molded product from a kneaded product of a metal powder and a binder; an assembling step of fitting the first molded product to the second molded product without performing a solvent degreasing treatment to form a composite; and a heating step of subjecting the composite to a thermal degreasing treatment and a sintering treatment, in which the first molded product and the second molded product have fitting portions that fit to each other, at least one of the fitting portion of the first molded product and the fitting portion of the second molded product has a tapered shape, in the assembling step, a maximum meshing when the fitting portion of the first molded product and the fitting portion of the second molded product are fitted to each other is 0.002 mm or more and 0.010 mm or less, and a content of the binder in the kneaded product is 2 mass % or more and 20 mass % or less with respect to a total amount of the kneaded product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a structure of a metal composite sintered body according to an embodiment.

FIG. 2 is a process flow diagram showing a method for manufacturing a metal composite sintered body.

FIG. 3 is a schematic cross-sectional view showing a structure of a first molded product.

FIG. 4 is a schematic cross-sectional view showing a structure of a second molded product.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

In each of the following figures, XYZ axes are attached as coordinate axes orthogonal to one another as necessary, a direction pointed by each arrow is a +direction, and a direction opposite to the +direction is a −direction. A +Z direction may be an upper side and a −Z direction may be a lower side, and a view viewed from the +Z direction or the −Z direction is referred to as a plan view. Further, in each of the following figures, a scale of each member is different from an actual scale for convenience of illustration.

EMBODIMENTS 1. Configuration of Metal Composite Sintered Body

In the present embodiment, a metal composite sintered body 1 formed of two members, a first molded product and a second molded product, is illustrated. The metal composite sintered body according to the present disclosure is not limited to being formed of two members, and may be formed of three or more members. A shape of the metal composite sintered body according to the present disclosure is not limited to shapes illustrated below. Hereinafter, a configuration of the metal composite sintered body 1 according to the embodiment will be described with reference to FIG. 1.

As shown in FIG. 1, the metal composite sintered body 1 is formed by combining a first molded product 10 and a second molded product 20. The first molded product 10 has a substantially circular cylindrical shape in a plan, and has openings at a lower side, an upper side, and a side surface. The second molded product 20 is formed to have a flat lower side and a circular upper side in the plan view from the +Z direction. The upper side of the second molded product 20 is inserted in a cylindrical inside of the first molded product 10 from the lower side.

The upper side of the second molded product 20 is inserted in the inside of the first molded product 10, and a substantially cylindrical inner side, that is, an inner surface of the first molded body 10 is in contact with a side surface of the upper side of the second molded product 20. In a region where the first molded product 10 and the second molded product 20 are in contact with each other, a first molded product 10 side is a fitting portion 13, and a second molded product 20 side is a fitting portion 23. The fitting portion 13 is a part of the inner surface of the first molded product 10. The fitting portion 23 is a part of the side surface of the second molded product 20. That is, the fitting portion 13 of the first molded product 10 and the fitting portion 23 of the second molded product 20 are fitted to each other.

The fitting portion 13 of the first molded product 10 has a shape that is rotationally symmetrical with respect to a central axis of a cylinder along the Z axis, except for the opening provided on the side surface. Further, the fitting portion 23 of the second molded product 20 has a shape that is also rotationally symmetrical with respect to the central axis along the Z axis and in which a part of the side surface of a solid is cut off. Therefore, the first molded product 10 and the second molded product 20 are fitted to each other such that central axes thereof coincide with each other.

The first molded product 10 and the second molded product 20 each contain a metal powder. Although details will be described later, the first molded product 10 and the second molded product 20 are assembled as the members of the metal composite sintered body 1 after being individually manufactured by injection-molding the metal powder.

2. Method for Manufacturing Metal Composite Sintered Body

A method for manufacturing the metal composite sintered body 1 according to the present embodiment will be described with reference to FIGS. 2, 3 and 4. Here, FIGS. 3 and 4 show a state of a single member before the first molded product 10 and the second molded product 20 are assembled to each other. Further, in FIGS. 3 and 4, the rotation central axes of the first molded product 10 and the second molded product 20 described above are included, and a cross section along an XZ plane is shown.

As shown in FIG. 2, the method for manufacturing the metal composite sintered body 1 includes steps S1 to S3. A process flow shown in FIG. 2 is an example and the present disclosure is not limited thereto.

Step S1 is a molding step. In step S1, the first molded product 10 and the second molded product 20 are injection-molded from a kneaded product of a metal powder and a binder. It is preferable to use metal injection mold (MIM) as an injection molding method. According to the metal injection mold, it is possible to mold a relatively small member or a member having a complicated and fine shape.

The metal powder can be sintered by a sintering treatment described later, and is not particularly limited as long as a material is a known molding material that can be used for the metal injection mold. Examples of such a molding material include a simple substance such as Fe, Ni, Co, Cr, Mn, Zn, Pt, Au, Ag, Cu, Pd, Al, W, Ti, V, Mo, Nb, Zr, Pr, Nd and Sm, or an alloy containing one or more of these substances as main components.

Examples of a Fe-based alloy include stainless steels such as austenite-based stainless steels, martensite-based stainless steels, and precipitation-hardened stainless steels, low-carbon steels, carbon steels, heat-resistant steels, die steels, high-speed tool steels, a Fe—Ni alloy, and a Fe—Ni—Co alloy.

Examples of a Ni-based alloy include a Ni—Cr—Fe-based alloy, a Ni—Cr—Mo-based alloy, and a Ni—Fe-based alloy.

Examples of a Co-based alloy include a Co—Cr-based alloy, a Co—Cr—Mo-based alloy, and a Co—Al—W-based alloy.

Examples of a Ti-based alloy include alloys of Ti with metal elements such as Al, V, Nb, Zr, Ta, and Mo, and specifically, Ti-6Al-4V, Ti-6Al-7Nb, or the like.

As the metal powder, a single molding material may be used alone, or two or more types including different molding materials may be mixed and used.

A reduction method, a carbonyl method, a pulverization method, or the like may be adopted for manufacturing the metal powder, and it is preferable to adopt an atomization method such as a water atomization method, a gas atomization method, or a high-speed rotating water flow atomization method. Accordingly, a metal powder having a relatively small average particle size can be manufactured at a low manufacturing cost. The metal powder may be subjected to a heat treatment, a plasma treatment, an ozone treatment, a reduction treatment or the like as a pretreatment.

The average particle size of the metal powder is not particularly limited, and is appropriately selected depending on fluidity in producing the kneaded product, moldability during the injection molding, dimensional stability of the metal composite sintered body 1, or the like. Specifically, for example, the average particle size is set to 3 μm or more and 30 μm or less. The average particle size in the present specification refers to a volume-based particle size distribution (50%). The average particle size is measured by a dynamic light scattering method or a laser diffracted light method described in JIS Z8825. Specifically, for example, a particle size distribution meter using the dynamic light scattering method as a measurement principle can be adopted.

A content of the metal powder in the kneaded product is not particularly limited, and is appropriately selected depending on the fluidity in producing the kneaded product, mechanical strength or the dimensional stability of the metal composite sintered body 1, or the like. Specifically, for example, the content is 80 mass % or more and 98 mass % or less, and preferably 85 mass % or more and 96 mass % or less, with respect to a total amount of the kneaded product.

The binder is not particularly limited as long as the binder does not chemically react with the metal powder. Specifically, examples include various resins such as a silicone resin, an epoxy resin, a phenol resin, a polyamide resin, a polyimide resin, and a polyphenylene sulfide resin, and organic materials such as long chain fatty acids, long chain fatty acid esters or wax esters, long chain fatty acid amides, and paraffin. As the binder, one or more of these components is adopted according to various requirements in a manufacturing process such as ease of thermal degreasing.

A content of the binder in the kneaded product is 2 mass % or more and 20 mass % or less, and preferably 4 mass % or more and 15 mass % or less, with respect to the total amount of the kneaded product. Accordingly, the mechanical strength of the first molded product 10 and the mechanical strength of the second molded product 20 up to a thermal degreasing treatment described later are secured. Further, since the content of the binder is not excessive, the binder can be easily removed in the thermal degreasing treatment.

In addition to the metal powder and the binder, the kneaded product may contain a sintering aid, inorganic powders such as ceramic powders and glass powders, and various additives such as a plasticizer, a lubricant, an antioxidant, a degreasing accelerator, and a surfactant.

The kneaded product is produced by dry-blending the above metal powder and the binder in advance and then performing kneading with a kneading machine such as a kneader. Kneading conditions in the kneading machine are not particularly limited. For example, a kneading temperature is 50° C. or higher and 200° C. or lower, and a kneading time is 15 minutes or longer and 3.5 hours or shorter. The kneaded product is then granulated and processed into pellets. A known device such as a pelletizer can be adopted for processing the kneaded product into the pellets.

Next, the first molded product 10 and the second molded product 20 are produced from the pellets by the metal injection mold. A known metal injection molding machine can be adopted for the metal injection mold. Molding molds corresponding to shapes of the first molded product 10 and the second molded product 20 are used.

Molding conditions in the metal injection mold are not particularly limited, and can be appropriately changed according to the type or the content of the metal powder or the binder. Specifically, for example, a material temperature is 80° C. or higher and 200° C. or lower, and an injection pressure is 20 kgf/cm² or more and 1500 kgf/cm² or less.

Here, detailed shapes of the first molded product 10 and the second molded product 20 produced by the metal injection mold will be described.

A taper is provided on the inner surface of the first molded product 10 including the fitting portion 13. Specifically, as shown in FIG. 3, the fitting portion 13 is arranged on a tapered surface whose lower side is widened at a gradient angle θ1. When the first molded product 10 is viewed in the plan view from the lower side, a lower end of the fitting portion 13 is a circle. Here, a diameter of the circle is defined as a distance L1.

A taper is also provided on the side surface of the second molded product 20 including the fitting portion 23. Specifically, as shown in FIG. 4, the fitting portion 23 is arranged on the tapered surface whose upper side is narrowed at a gradient angle θ2. When the second molded product 20 is viewed in the plan view from the upper side, a lower end of the fitting portion 23 is a circle. Here, a diameter of the circle is defined as a distance L2.

The distance L2 is larger than the distance L1. In the subsequent step S2, a maximum meshing {(L2−L1)/2} when the fitting portion 13 and the fitting portion 23 are fitted to each other is 0.002 mm or more and 0.010 mm or less.

A difference (θ2−θ1) in gradient angles between the fitting portion 13 of the first molded product 10 and the fitting portion 23 of the second molded product 20 is 0.5° or more and 5.0° or less, and preferably 1.0° or more and 3.0° or less. Accordingly, in step S2, the first molded product 10 and the second molded product 20 can be more steadily assembled to each other.

Here, in the present embodiment, the embodiment in which the fitting portion 13 and the fitting portion 23 both have a tapered shape is illustrated, but the present disclosure is not limited thereto. At least one of the fitting portions 13 and 23 may have the tapered shape.

Further, the fitting portions 13 and 23 may each be provided with a positioning portion for preventing a deviation during fitting in the subsequent step S2. An example of the positioning portion is a D-cut. Specifically, the D-cut is provided in the fitting portion 23, and a flat surface portion corresponding to the D-cut is provided in the fitting portion 13. A shape of the positioning portion is not limited to the above. According to the positioning portion, in step S2, positioning of the first molded product 10 and the second molded product 20 can be facilitated, and the first molded product 10 and the second molded product 20 can be made difficult to deviate from each other. After individually producing the first molded product 10 and the second molded product 20, the process proceeds to step S2.

Step S2 is an assembling step. In step S2, the first molded product 10 and the second molded product 20 are formed into a composite without performing a solvent degreasing treatment. Since the first molded product 10 and the second molded product 20 are assembled into the composite without performing the degreasing treatment, the composite has higher strength and is easier to handle than a case where the first molded product 10 and the second molded product 20 are assembled to each other after the degreasing treatment. Further, the assembled composite is similarly maintained in strength and easy to handle until the thermal degreasing treatment in the subsequent step S3 is performed.

Since the first molded product 10 and the second molded product 20 have the above characteristics, in addition to improving the workability of the assembly in this step S2, the first molded product 10 and the second molded product 20 are appropriately fitted to each other without being too loose or too tight. Then, the process proceeds to step S3.

Step S3 is a heating step. In step S3, the composite is first subjected to the thermal degreasing treatment. In the thermal degreasing treatment, the binder contained in the composite is removed or reduced by heating. The thermal degreasing treatment is simpler than the solvent degreasing treatment using an organic solvent or the like in that a waste liquid treatment for the used solvent is unnecessary.

The binder in the composite is volatilized by the thermal degreasing treatment. At the end of the heat degreasing treatment, a part of the binder may remain in the composite. Such residues are removed by heating at a higher temperature in the subsequent sintering treatment.

In the thermal degreasing treatment, the composite is heated at 400° C. or higher and 550° C. or lower for 30 minutes or longer and 6 hours or shorter. The heating temperature is preferably 430° C. or higher and 520° C. or lower, and the heating time is preferably 1 hour or longer and 4 hours or shorter. Accordingly, the binder contained in the first molded product 10 and the second molded product 20 can be efficiently removed or reduced.

An atmosphere in the thermal degreasing treatment is not particularly limited, and examples thereof include an inert gas atmosphere containing nitrogen gas or argon gas, and a reduced pressure atmosphere in which an optional gas is depressurized. Of these atmospheres, the reduced pressure atmosphere is preferred. Accordingly, oxidation of the metal powder contained in the composite is prevented.

Next, after the heat degreasing treatment, the sintering treatment is performed. The composite subjected to the thermal degreasing treatment becomes the metal composite sintered body 1 by the sintering treatment. Specifically, the metal powder in the composite is diffused and grain-grown to form crystal grains, and the metal composite sintered body 1 having a high density and a low porosity as a whole can be obtained. At this time, in a region where the first molded product 10 and the second molded product 20 are in contact with each other, including the fitting portion 13 and the fitting portion 23, the above diffusion and grain growth proceed, so that the first molded product 10 and the second molded product 20 are integrated by diffusion bonding.

In the sintering treatment, the composite is heated at 900° C. or higher and 1500° C. or lower for 30 minutes or longer and 8 hours or shorter. The heating temperature is preferably 950° C. or higher and 1450° C. or lower, and the heating time is preferably 1 hour or longer and 5 hours or shorter. Accordingly, the diffusion bonding by sintering is promoted between the first molded product 10 and the second molded product 20. Therefore, the first molded product 10 and the second molded product 20 can be firmly integrated to each other while preventing an occurrence of detachment, or the like.

An atmosphere in the sintering treatment is not particularly limited, and examples thereof include an oxidizing gas atmosphere containing oxygen gas, air, or the like, a reducing gas atmosphere containing hydrogen gas, ammonia decomposition gas, or the like, an inert gas atmosphere containing nitrogen gas, argon gas, or the like, and a reduced pressure atmosphere in which an optional gas is depressurized. Of these atmospheres, the reducing gas atmosphere or the inert gas atmosphere is preferred, and the reduced pressure atmosphere is more preferred. Accordingly, the oxidation of the metal powder contained in the composite is prevented.

Examples of a specific atmosphere in the sintering treatment include a reduced pressure atmosphere of 1.3×10⁻³ Pa to 1.3 Pa, an inert gas atmosphere, such as nitrogen gas or argon gas atmosphere, of 1.3×10² Pa to 1.0×10⁴ Pa, and a hydrogen gas atmosphere of 1.3×10⁴ Pa to 1.0×10⁶ Pa.

The atmosphere in the sintering treatment may change during the treatment. For example, after the atmosphere is changed into a reduced pressure atmosphere of 1.3×10⁻⁴ Pa to 1.0×10⁴ Pa, the atmosphere is switched to the above inert gas atmosphere.

The sintering treatment may be a stepwise treatment of two or more stages. For example, a primary treatment and a secondary treatment having different treatment conditions may be combined. In this case, a heating temperature in the secondary treatment is set higher than a heating temperature in the primary treatment. Further, the thermal degreasing treatment and the sintering treatment may be carried out individually or continuously. The metal composite sintered body 1 is manufactured through the above manufacturing steps.

According to the present embodiment, the following effects can be obtained.

In the metal composite sintered body 1, the workability can be improved and the quality can be stabilized. Specifically, since the first molded product 10 and the second molded product 20 are assembled to each other without performing the solvent degreasing treatment, the binder is not removed, the strength is maintained, and handling is easier. Then, since the thermal degreasing treatment and the sintering treatment are performed after the assembling step S2, an occurrence of damage or the like can be prevented.

Since the tapered shapes of the fitting portions 13 and 23 and the maximum meshing of the fitting portions 13 and 23 are within a predetermined range, the first molded product 10 and the second molded product 20 are appropriately fitted to each other without being too loose or too tight. Therefore, the first molded product 10 and the second molded product 20 are steadily assembled to each other, and the occurrence of the damage such as cracking due to the fitting is prevented. From the above, it is possible to provide the metal composite sintered body 1 having excellent workability and stable quality. 

What is claimed is:
 1. A method for manufacturing a metal composite sintered body, comprising: a molding step of injection-molding a first molded product and a second molded product from a kneaded product of a metal powder and a binder; an assembling step of fitting the first molded product to the second molded product without performing a solvent degreasing treatment to form a composite; and a heating step of subjecting the composite to a thermal degreasing treatment and a sintering treatment, wherein the first molded product and the second molded product have fitting portions that fit to each other, at least one of the fitting portion of the first molded product and the fitting portion of the second molded product has a tapered shape, in the assembling step, a maximum meshing when the fitting portion of the first molded product and the fitting portion of the second molded product are fitted to each other is 0.002 mm or more and 0.010 mm or less, and a content of the binder in the kneaded product is 2 mass % or more and 20 mass % or less with respect to a total amount of the kneaded product.
 2. The method for manufacturing a metal composite sintered body according to claim 1, wherein a difference in gradient angles between the fitting portion of the first molded product and the fitting portion of the second molded product is 0.5° or more and 5.0° or less.
 3. The method for manufacturing a metal composite sintered body according to claim 1, wherein the fitting portion of the first molded product and the fitting portion of the second molded product are each provided with a positioning portion for preventing a deviation during fitting in the assembling step.
 4. The method for manufacturing a metal composite sintered body according to claim 1, wherein in the thermal degreasing treatment, heating at 400° C. or higher and 550° C. or lower is performed for 30 minutes or longer and 6 hours or shorter.
 5. The method for manufacturing a metal composite sintered body according to claim 1, wherein in the sintering treatment, heating at 900° C. or higher and 1500° C. or lower is performed for 30 minutes or longer and 8 hours or shorter. 